Approximately 28,000 individuals in North America have a subarachnoid hemorrhage from a ruptured intracranial aneurysm each year. Unlike most other forms of stroke, aneurysmal subarachnoid hemorrhage affects younger adults who have the potential for returning to many years of vigorous, productive life. This potential is currently not being realized. Although nearly 80% of the individuals suffering a subarachnoid hemorrhage enter the hospital in good neurological condition, only 56% will recover to their premorbid state without neurological deficits. The leading cause of death and disability is focal cerebral ischemia resulting from vasospasm. An effective therapy for vasospasm has proven elusive and could salvage approximately 5,000 lives per year. The newer calcium channel blocking agents with cerebral vascular specificity have a number of properties which suggest that they may be useful in the management of cerebral vasospasm. While the results of laboratory and small clinical studies have been promising, definition of the role of these agents is controversial and awaits scientific confirmation. The Cooperative Aneurysm Study proposes to examine the safety and efficacy of the calcium channel blocking agent, nicardipine hydrochloride, in improving outcome in patients with aneurysmal subarachnoid hemorrhage by conducting a large scale, randomized, placebo-controlled, double-blind clinical trial in 1600 patients with aneurysmal subarachnoid hemorrhage admitted to approximately 30 neurosurgical centers in North America. Outcome measures will include neurological and disability status and cerebral infarction rate at three months following subarachnid hemorrhage and the occurrence of symptomatic vasospasm during the acute period following aneurysm rupture. A novel funding approach will be utilized whereby the cost of the study will be shared between NIH and Syntex, Inc., thus satisfying the needs of both public and private sectors in an economical manner.